JP5766519B2 - I / O device - Google Patents

Description

One embodiment of the present invention relates to an input / output device. One embodiment of the present invention relates to a method for driving an input / output device.

In recent years, technological development of an apparatus (also referred to as an input / output apparatus) having a function of outputting information and a function of inputting information by incidence of light has been advanced.

As an input / output device, an input / output device including a backlight including a plurality of light detection circuits (also referred to as photosensors) arranged in a matrix direction in a pixel portion and a light emitting diode of a plurality of colors as a light source can be given. (For example, patent document 1). In the input / output device described in Patent Document 1, the backlight is turned on by switching the color of emitted light in each frame period, a full-color image is displayed, and reflected light from an object to be read is read as data. Therefore, the input / output device disclosed in Patent Document 1 functions as a touch panel. Note that a method in which the backlight is turned on by switching the color of emitted light during each frame period is also referred to as a field sequential method.

JP-A-11-008741

Conventional input / output devices have a problem of low light detection accuracy.

For example, a conventional input / output device is a method (also referred to as a rolling shutter method) that generates and outputs data (also referred to as optical data) corresponding to the illuminance of incident light for each light detection circuit in each row. Further, in the case of the field sequential method, the conventional input / output device has to switch a plurality of light emitting diodes in order to emit light and switch the lighting state of the backlight in one frame period. Therefore, in order to generate optical data corresponding to each lighting state of the backlight, optical data is generated for each photodetection circuit in each row during each lighting state, and the optical data is generated in all the photodetection circuits. When the optical data is generated, the time during which light is incident on each photodetection circuit is short, and the light detection accuracy is low.

Further, for example, light in an environment where the input / output device such as external light is placed enters the input / output device. For this reason, when the optical data is generated, the light in the environment becomes noise, so that the light detection accuracy is lowered. For example, when information is input to the input / output device when the reflected light of the finger enters the light detection circuit, such as a touch panel, the reflected light of the hand other than the finger and the reflected light of the finger are It may be identified as equivalent information by the light in the environment where it is placed.

An object of one embodiment of the present invention is to improve light detection accuracy.

One embodiment of the present invention is a light guide plate through which light from a display circuit, a plurality of light detection circuits, a first light unit including a plurality of first light emitting diodes, a second light emitting diode, and a second light emitting diode is incident. The first light unit is turned on by switching a plurality of first light emitting diodes for each unit period to emit light, and the first light unit is turned off when the first light unit is turned off. The second light unit is turned on by causing the two light emitting diodes to emit light, and optical data is generated in a plurality of light detection circuits according to the same signal when the second light unit is turned on in a unit period. is there. This suppresses the influence of light in the environment where the input / output device is placed.

One embodiment of the present invention is a first light unit including Z light emitting diodes (Z is a natural number of 3 or more), and a second light unit including a white light emitting diode and a light guide plate on which light from the white light emitting diode is incident. Are provided between the first light unit and the second light unit, the display selection signal is input, the display data signal is input according to the display selection signal, and the display state according to the data of the input display data signal Is provided between the X display circuits (X is a natural number) and the first light unit and the second light unit, and the same light detection control signal is input to each, and according to the input light detection control signal And an Y number (Y is a natural number of 2 or more) photodetection circuits that generate data corresponding to the illuminance of incident light.

One embodiment of the present invention is a first light unit including Z light emitting diodes (Z is a natural number of 3 or more), and a second light unit including a white light emitting diode and a light guide plate on which light from the white light emitting diode is incident. Are provided between the first light unit and the second light unit, the display selection signal is input, the display data signal is input according to the display selection signal, and the display state according to the data of the input display data signal Is provided between the X display circuits (X is a natural number) and the first light unit and the second light unit, and a light detection control signal is input and incident according to the input light detection control signal A method of driving an input / output device comprising Y (Y is a natural number greater than or equal to 2) photodetector circuits that generate data according to the illuminance of light, each of the Y photodetector circuits The same light detection control signal is input to the first light unit, and the first light unit is turned off by sequentially switching the Z light emitting diodes to emit light during the frame period set by the display selection signal. The second light unit is turned on by causing the white light emitting diode to emit light in the state, and according to the illuminance of light incident on the Y light detection circuits during the period in which the second light unit is in the lighting state This is a driving method of an input / output device that generates Y data.

One embodiment of the present invention is a first light unit including Z light emitting diodes (Z is a natural number of 3 or more), and a second light unit including a white light emitting diode and a light guide plate on which light from the white light emitting diode is incident. Are provided between the first light unit and the second light unit, the display selection signal is input, the display data signal is input according to the display selection signal, and the display state according to the data of the input display data signal Is provided between the X display circuits (X is a natural number) and the first light unit and the second light unit, and a light detection control signal is input and incident according to the input light detection control signal A method of driving an input / output device comprising Y (Y is a natural number greater than or equal to 2) photodetector circuits that generate data according to the illuminance of light, each of the Y photodetector circuits The same light detection control signal is input to the first light unit, and the first light unit is turned off by sequentially switching the Z light emitting diodes to emit light during the frame period set by the display selection signal. The second light unit is turned on by causing the white light emitting diode to emit light in the state, and according to the illuminance of light incident on the Y light detection circuits during the period in which the second light unit is in the lighting state Y pieces of first data are generated, and Y pieces of second data corresponding to the illuminance of light incident on the Y pieces of light detection circuits during a period in which the first light unit and the second light unit are turned off. A method of driving an input / output device that further includes generating third data, and generating third data that is difference data between the first data and the second data.

According to one embodiment of the present invention, light detection accuracy can be improved.

4A and 4B illustrate an example of an input / output device in Embodiment 1. FIG. 5 illustrates an example of an input / output device in Embodiment 2. FIG. 6 illustrates an example of a light detection circuit in Embodiment 3; FIG. 10 illustrates an example of a display circuit in Embodiment 4; FIG. 6 is a schematic cross-sectional view illustrating a structural example of a light unit in a fifth embodiment. 7 is a schematic cross-sectional view illustrating a structural example of a transistor in Embodiment 6. FIG. FIG. 7 is a schematic cross-sectional view illustrating a method for manufacturing the transistor illustrated in FIG. The figure for demonstrating a characteristic evaluation circuit. The figure which shows the relationship between the elapsed time Time concerning the measurement in sample 4 (SMP4), sample 5 (SMP5), and sample 6 (SMP6), the output voltage Vout, and the leak current calculated by the measurement. The figure which shows the relationship between the voltage of the node A estimated by measurement, and leakage current. The figure which shows the relationship between the voltage of the node A estimated by measurement, and leakage current. The figure which shows the relationship between the voltage of the node A estimated by measurement, and leakage current. The figure which shows the relationship between the voltage of the node A estimated by measurement, and leakage current. FIG. 10 shows a structure example of an active matrix substrate in Embodiment 7. FIG. 10 shows a structure example of an active matrix substrate in Embodiment 7. FIG. 10 illustrates a structure example of an input / output device in Embodiment 7; FIG. 9 illustrates a configuration example of an electronic device in Embodiment 8.

An example of an embodiment for explaining the present invention will be described below with reference to the drawings. However, the present invention is not limited to the following description, and it is easily understood by those skilled in the art that modes and details can be variously changed without departing from the spirit and scope of the present invention. Therefore, the present invention should not be construed as being limited to the description of the embodiments below.

Note that the contents of the embodiments can be combined with each other as appropriate. Further, the contents of the embodiments can be replaced with each other.

(Embodiment 1)
In this embodiment, an input / output device that can output information and can input information by incident light will be described.

An example of the input / output device in this embodiment is described with reference to FIGS. FIG. 1 is a diagram for describing an example of an input / output device according to this embodiment.

First, a structure example of the input / output device in this embodiment is described with reference to FIG. FIG. 1A is a schematic diagram illustrating a configuration example of an input / output device in this embodiment.

An input / output device illustrated in FIG. 1A includes a display selection signal output circuit (also referred to as DSELOUT) 101, a display data signal output circuit (also referred to as DDOUT) 102, and a light detection reset signal output circuit (also referred to as PRSTOUT) 103a. A light detection control signal output circuit (also referred to as PCTLOUT) 103b, an output selection signal output circuit (also referred to as OSELOUT) 103c, a light unit (also referred to as LIGHT) 104a, and light units 104b, and X (X is a natural number) ) Display circuit (also referred to as DISP) 105d, Y photodetection circuit (also referred to as PS) 105p (Y is a natural number of 2 or more), and readout circuit (also referred to as READ) 106.

The display selection signal output circuit 101 has a function of outputting a plurality of display selection signals (also referred to as a signal DSEL) that are pulse signals.

The display selection signal output circuit 101 includes a shift register, for example. The display selection signal output circuit 101 can output a display selection signal by outputting a pulse signal from the shift register.

The display data signal output circuit 102 receives an image signal representing an image as an electrical signal. The display data signal output circuit 102 has a function of generating a display data signal (also referred to as a signal DD) that is a voltage signal based on the input image signal and outputting the generated display data signal.

The display data signal output circuit 102 includes a transistor, for example.

Note that in the input / output device, the transistor includes two terminals and a current control terminal that controls a current flowing between the two terminals by an applied voltage. In addition, not only a transistor but the terminal by which the electric current which flows between each other is controlled is also called a current terminal, and each of two current terminals is also called a 1st current terminal and a 2nd current terminal.

In the input / output device, for example, a field effect transistor can be used as the transistor. In the case of a field effect transistor, the first current terminal is one of a source and a drain, the second current terminal is the other of the source and the drain, and the current control terminal is a gate.

In general, a voltage refers to a difference in potential between two points (also referred to as a potential difference). However, the values of voltage and potential are both expressed in volts (V) in circuit diagrams and the like, and thus are difficult to distinguish. Therefore, in this specification, a potential difference between a potential at one point and a reference potential (also referred to as a reference potential) may be used as the voltage at the one point unless otherwise specified.

The display data signal output circuit 102 can output image signal data as a display data signal when the transistor is on. The transistor can be controlled by inputting a control signal which is a pulse signal to the current control terminal. Note that in the case where there are a plurality of display circuits 105d, image signal data may be output as a plurality of display data signals by selectively turning on or off a plurality of transistors.

The light detection reset signal output circuit 103a has a function of outputting a light detection reset signal (also referred to as a signal PRST) that is a pulse signal.

The light detection reset signal output circuit 103a includes, for example, a shift register. The light detection reset signal output circuit 103a can output a light detection reset signal by outputting a pulse signal from the shift register.

The light detection control signal output circuit 103b has a function of outputting a light detection control signal (also referred to as a signal PCTL) that is a pulse signal.

The light detection control signal output circuit 103b includes a shift register, for example. The light detection control signal output circuit 103b can output a light detection control signal by outputting a pulse signal from the shift register.

The output selection signal output circuit 103c has a function of outputting an output selection signal (also referred to as a signal OSEL) that is a pulse signal.

The output selection signal output circuit 103c includes, for example, a shift register. The output selection signal output circuit 103c can output an output selection signal by outputting a pulse signal from the shift register.

The light unit 104a and the light unit 104b are light emitting units including a light source.

The light unit 104a includes Z light emitting diodes (also referred to as LEDs) A (Z is a natural number of 3 or more) as light sources. The Z light emitting diodes A are light emitting diodes that emit light having a wavelength in the visible light region (for example, a region having a wavelength of 360 nm or more and 830 nm or less). As the Z light emitting diodes A, for example, a red light emitting diode, a green light emitting diode, and a blue light emitting diode can be used. The number of light emitting diodes of each color may be plural. In addition to the red, green, and blue light emitting diodes, other light emitting diodes (for example, white light emitting diodes) may be used as the Z light emitting diodes A.

For example, the light emission of the light emitting diode A may be controlled using a control signal for selecting the light emitting diode A to which a voltage is applied. In addition, a light control circuit that outputs a control signal for controlling whether or not to select the light emitting diode A to which the voltage is applied may be provided in the light unit 104a.

The light unit 104b includes a light emitting diode B as a light source and a light guide plate. The light emitting diode B is a light emitting diode that emits light having a wavelength in the visible light region. As the light emitting diode, for example, a white light emitting diode can be used. The number of white light emitting diodes may be plural. The light from the light emitting diode B is incident on the light guide plate.

By configuring the light unit 104b as described above, for example, when the light object is in contact with the light guide plate when the light unit 104b is in a lighting state, light from the light source is transmitted at the contact portion between the object to be read and the light guide plate. The light is scattered and enters the light detection circuit 105p.

For example, the light emission of the light emitting diode B may be controlled using a control signal for selecting the light emitting diode B to which the voltage is applied. In addition, a light control circuit that outputs a control signal for controlling whether or not to select the light emitting diode B to which the voltage is applied may be provided in the light unit 104b.

The display circuit 105d is provided between the light unit 104a and the light unit 104b. In addition, a display selection signal which is a pulse signal is input to the display circuit 105d, and a display data signal is input in accordance with the input display selection signal. The display circuit 105d has a function of entering a display state according to the data of the input display data signal.

The display circuit 105d includes a display selection transistor and a display element, for example.

The display selection transistor has a function of selecting whether or not to input display data signal data to the display element.

The display element has a function of entering a display state corresponding to the data of the display data signal when the data of the display data signal is input according to the display selection transistor.

As the display element, for example, a liquid crystal element or the like can be used.

In addition, as a display method of an input / output device including a liquid crystal element, a TN (Twisted Nematic) mode, an IPS (In Plane Switching) mode, an STN (Super Twisted Nematic) mode, a VA (Vertical Alignment Alignment) mode, and an ASM (Axially Aligned Alignment) mode are used. Micro-cell) mode, OCB (Optically Compensated Birefringence) mode, FLC (Ferroelectric Liquid Crystal) mode, AFLC (Anti-Ferroelectric Liquid Crystal) mode, MVA (Multi-Antual Liquid Crystal mode) PVA (Patterned Vertical Alignment) mode, ASV (Advanced Super View) mode, FFS (Fringe Field Switching) mode, or the like may be used.

The light detection circuit 105p is provided between the light unit 104a and the light unit 104b. A light detection reset signal, a light detection control signal, and an output selection signal are input to the light detection circuit 105p.

The light detection circuit 105p has a function of entering a reset state in accordance with a light detection reset signal.

The photodetection circuit 105p has a function of generating data (also referred to as optical data) that is a voltage corresponding to the illuminance of incident light in accordance with the photodetection control signal.

The photodetection circuit 105p has a function of outputting the generated optical data as an optical data signal in accordance with the output selection signal.

The light detection circuit 105p includes, for example, a photoelectric conversion element (also referred to as a PCE), a light detection reset selection transistor, a light detection control transistor, an amplification transistor, and an output selection transistor.

The photoelectric conversion element has a function of causing a current (also referred to as a photocurrent) to flow according to the illuminance of incident light when light enters the photoelectric conversion element.

A photodetection reset signal is input to the current control terminal of the photodetection reset selection transistor. The photodetection reset selection transistor has a function of selecting whether or not to set the voltage of the current control terminal of the amplification transistor to a reference value.

A light detection control signal is input to the current control terminal of the light detection control transistor. The photodetection control transistor has a function of controlling whether or not the voltage of the current control terminal of the amplification transistor is set to a value corresponding to the photocurrent flowing through the photoelectric conversion element.

An output selection signal is input to the current control terminal of the output selection transistor. The output selection transistor has a function of selecting whether to output optical data from the light detection circuit 105p as an optical data signal.

The photodetection circuit 105p outputs optical data as an optical data signal from the first current terminal or the second current terminal of the amplification transistor.

Note that the display circuit 105 d and the light detection circuit 105 p are provided in the pixel portion 105. The pixel unit 105 is an area for displaying and reading information. Note that a pixel is constituted by one or more display circuits 105d. One or more light detection circuits 105p may be included in the pixel. Further, when the number of the display circuits 105d is plural, the display circuits 105d may be arranged in the matrix direction in the pixel portion 105, for example. Further, when the number of the light detection circuits 105p is plural, the light detection circuits 105p may be arranged in the matrix direction in the pixel portion 105, for example.

The reading circuit 106 has a function of selecting the photodetection circuit 105p that reads out optical data and reading out the optical data from the selected photodetection circuit 105p.

The read circuit 106 is configured using, for example, a selection circuit. For example, the selection circuit includes a transistor. The selection circuit can read out optical data when an optical data signal is input from the photodetection circuit 105p according to the transistor, for example.

Next, as an example of a method for driving the input / output device in this embodiment, an example of a method for driving the input / output device illustrated in FIG. 1A will be described with reference to FIGS. 1B and 1C are timing charts for explaining an example of a method for driving the input / output device illustrated in FIG.

In the example of the driving method of the input / output device illustrated in FIG. 1A, the same light detection control signal is input to the Y light detection circuits 105p. Further, in the frame period (for example, the frame period f1 to the frame period fn shown in FIGS. 1B and 1C) set according to the display selection signal, the Z light emitting diodes in the light unit 104a are sequentially switched. The light unit 104a is sequentially switched from the lighting state C1 (the state where the first light emitting diode A emits light) to the lighting state Ck (the state where the Zth light emitting diode A emits light). Note that in FIGS. 1B and 1C, a period between two consecutive lighting states of the light unit 104a is turned off.

Further, when a display data signal is input to the display circuit 105d in accordance with the display selection signal and the light unit 104a is in a lighting state, the display circuit 105d enters a display state corresponding to the data of the display data signal. For example, when the light unit 104a is in the lighting state C1, the display state of the display circuit 105d is the display state dc1 (display state based on the lighting state C1), and when the light unit 104a is in the lighting state C2, the display circuit 105d. Is in the display state dc2 (display state based on the lighting state C2), and when the light unit 104a is in the lighting state Ck, the display circuit 105d is in the display state dck (display state based on the lighting state Ck).

Further, when the light unit 104a is turned off, the light emitting diode B is caused to emit light and the light unit 104b is turned on. In addition, it is preferable that the cycle in which the light unit 104b switches from the light-off state to the light-on state is greater than 0 seconds and 1/60 seconds or less. Thereby, flickering of the display image due to blinking of the light unit 104b can be suppressed.

When the light unit 104b is in the lighting state LT, a light detection control signal pulse (also referred to as pls) is input to the Y light detection circuits 105p. At this time, each of the Y photodetection circuits 105p generates optical data. Note that, by setting the pulse period of the light detection control signal to be longer than the period in which the lighting state of the light unit 104a is switched, for example, a period in which optical data is not output when the light unit 104a is in the off state can be provided. . Therefore, when the optical data is generated, the period in which the light unit 104a is in the extinguished state can be fully used. Therefore, when generating the optical data, the time during which light is incident is set longer for each photodetector circuit. be able to. In addition, since optical data can be output regardless of the lighting state of the light unit, the operating frequency of the light detection circuit can be reduced, and power consumption can be reduced.

Further, according to the output selection signal, the Y photodetection circuits 105p output the generated optical data as an optical data signal, and read the optical data by inputting the optical data signal in the reading circuit 106.

Note that the timing of lighting the light unit 104b may be the same or different for each frame period.

For example, in the timing chart shown in FIG. 1B, optical data is generated by the light detection circuit 105p in a period in which the light unit 104a is turned off between the lighting state C1 and the lighting state C2 for each frame period. .

For example, in the timing chart shown in FIG. 1C, light data is generated by the light detection circuit 105p in a period in which different light units 104a are turned off for each frame period.

As described with reference to FIG. 1, an example of the input / output device in this embodiment includes a display circuit, a plurality of photodetector circuits, a first light unit, and a second light unit. The light unit includes a light guide plate on which light from a light source is incident. With the above configuration, the light detection accuracy can be improved because the reflected light from the read object can be incident on the light detection circuit only when the read object contacts the light guide plate in the second light unit. Can be made.

Furthermore, an example of the input / output device in this embodiment has a structure in which the same light detection control signal is input to Y light detection circuits. With the above configuration, the time required for all the photodetection circuits to generate optical data can be shortened, and the time during which light is incident on each photodetection circuit is set long when generating optical data. In addition, the operating frequency of the photodetection circuit can be reduced and power consumption can be reduced. A method of inputting the same light detection control signal to a plurality of light detection circuits is also referred to as a global shutter method.

Furthermore, an example of the input / output device in this embodiment has a configuration in which the first light unit is turned on by sequentially switching a plurality of light emitting diodes to emit light in each frame period. With the above structure, a full color image can be displayed in the input / output device.

Further, in the example of the input / output device in this embodiment, the same light detection control signal is input to the Y light detection circuits so that the second light unit is turned on when the first light unit is turned off. In addition, when the second light unit is in a lighting state, optical data can be generated in a plurality of light detection circuits. With the above configuration, it is possible to suppress the influence on the display image by the first light unit and the second light unit. Moreover, the influence on the optical data by a display image can be suppressed.

Therefore, with the above configuration, the light detection accuracy can be improved.

(Embodiment 2)
In this embodiment, another example of the input / output device of Embodiment 1 is described. In addition, about the same part as the said Embodiment 1, description of Embodiment 1 is used suitably.

An example of the input / output device in this embodiment is described with reference to FIGS. FIG. 2 is a diagram for describing an example of the input / output device according to this embodiment.

First, a structure example of the input / output device in this embodiment is described with reference to FIG. FIG. 2A is a schematic diagram illustrating a configuration example of the input / output device in this embodiment.

2A includes a display selection signal output circuit 101, a display data signal output circuit 102, a light detection reset signal output circuit 103a, a light detection control signal output circuit 103b, and an output selection signal output. A circuit 103c, a light unit 104a, a light unit 104b, X display circuits 105d, Y photodetection circuits 105p, a readout circuit 106, and a data processing circuit (also referred to as DataP) 107 are provided. .

Display selection signal output circuit 101, display data signal output circuit 102, light detection reset signal output circuit 103a, light detection control signal output circuit 103b, output selection signal output circuit 103c, light unit 104a, light unit 104b, display circuit 105d, light Since the detection circuit 105p and the reading circuit 106 are the same as the input / output device illustrated in FIG. 1A, the description of each component of the input / output device illustrated in FIG.

The data processing circuit 107 is a circuit that performs arithmetic processing on data of an input data signal. The data processing circuit 107 includes a storage circuit and an arithmetic circuit. The memory circuit has a function of storing data of data signals, and the arithmetic circuit has a function of generating difference data of data of a plurality of data signals by arithmetic processing.

The data processing circuit 107 may be provided in the input / output device, or the input / output device is electrically connected to data processing means (such as a personal computer) having the same function as the separately provided data processing circuit. A configuration may be adopted. By providing the data processing circuit 107 in the input / output device, the number of wirings in the connection portion between the data processing circuit 107 and the reading circuit 106 can be reduced.

Next, as an example of a method for driving the input / output device in this embodiment, an example of a method for driving the input / output device illustrated in FIG. 2A will be described with reference to FIG. FIG. 2B is a timing chart for explaining an example of a method for driving the input / output device illustrated in FIG.

In the example of the driving method of the input / output device illustrated in FIG. 2A, the same light detection control signal is input to the Y light detection circuits 105p. Further, in the frame period (for example, the frame period f1 to the frame period fn shown in FIG. 2B) set in accordance with the display selection signal, the first light-emitting diode A to the Z-th light-emitting diode A in the light unit 104a are changed. As shown in FIG. 2B, the light unit 104a is turned on in order from the lighting state C1 (the state where the first light emitting diode A emits light) to the lighting state Ck (when the Zth light emitting diode A is turned on). Switch to the flashing state. Further, the light unit 104a is turned off during each lighting state.

Further, when the display data signal is input to the display circuit 105d in accordance with the display selection signal and the light unit 104a is in the lighting state, the display circuit 105d enters a display state corresponding to the data of the display data signal. For example, when the light unit 104a is in the lighting state C1, the display state of the display circuit 105d is the display state dc1 (display state based on the lighting state C1), and when the light unit 104a is in the lighting state C2, the display circuit 105d is When the light unit 104a is in the lighting state Ck, the display circuit 105d is in the display state dck (display state based on the lighting state Ck).

Further, when the light unit 104a is turned off, the light emitting diode B is caused to emit light and the light unit 104b is turned on.

When the light unit 104b is in a lighting state, a pulse of the light detection control signal is input to the Y light detection circuits 105p. At this time, each of the Y photodetection circuits 105p generates optical data.

Further, according to the output selection signal, the Y photodetection circuits 105p output the generated optical data as an optical data signal, and read the optical data by inputting the optical data signal in the reading circuit 106. The read optical data is stored in the storage circuit in the data processing circuit 107.

Further, in a frame period different from the above-described frame period (frame period fn in FIG. 2B), when the light unit 104a and the light unit 104b are turned off, the light detection control signal pulse has Y light detections. Input to the circuit 105p. At this time, each of the Y photodetection circuits 105p generates optical data.

Further, according to the output selection signal, the Y photodetection circuits 105p output the generated optical data as an optical data signal, and read the optical data by inputting the optical data signal in the reading circuit 106. The read optical data is stored in the storage circuit in the data processing circuit 107.

Further, the arithmetic circuit in the data processing circuit 107 generates difference data between the optical data when the light unit 104b is in the on state and the optical data when the light unit 104a and the light unit 104b are in the off state. The difference data is used as data for executing a predetermined process.

As described with reference to FIG. 2, the example of the input / output device in this embodiment includes the optical data when the second light unit is in the lighting state and the first data in addition to the configuration shown in the first embodiment. Optical data when the light unit and the second light unit are turned off is generated, and difference data between the two optical data signals is generated. By generating the difference data, in addition to the effects shown in the first embodiment, the light information in the environment where the input / output device is placed can be removed from the optical data, so that the light detection accuracy is further improved. be able to.

(Embodiment 3)
In this embodiment, an example of a photodetector circuit in the input / output device of the above embodiment will be described.

An example of the photodetector circuit in this embodiment will be described with reference to FIGS. FIG. 3 is a diagram for describing an example of the photodetector circuit in this embodiment.

First, structural examples of the photodetector circuit in this embodiment will be described with reference to FIGS. 3A and 3B are diagrams each illustrating an example of a structure of the photodetector circuit in this embodiment.

The photodetector circuit illustrated in FIG. 3A includes a photoelectric conversion element 131a, a transistor 132a, a transistor 133a, and a transistor 134a.

Note that in the photodetector circuit illustrated in FIG. 3A, the transistor 132a, the transistor 133a, and the transistor 134a are field-effect transistors.

The photoelectric conversion element 131a has a first current terminal and a second current terminal, and a reset signal is input to the first current terminal of the photoelectric conversion element 131a.

One of a source and a drain of the transistor 134a is electrically connected to the second current terminal of the photoelectric conversion element 131a, and a light detection control signal is input to a gate of the transistor 134a.

The gate of the transistor 132a is electrically connected to the other of the source and the drain of the transistor 134a.

One of a source and a drain of the transistor 133a is electrically connected to one of a source and a drain of the transistor 132a, and an output selection signal is input to a gate of the transistor 133a.

Note that the voltage Va is input to the other of the source and the drain of the transistor 132a and the other of the source and the drain of the transistor 133a.

The photodetector circuit illustrated in FIG. 3A outputs optical data as an optical data signal from the other of the source and the drain of the transistor 132a and the other of the source and the drain of the transistor 133a.

The photodetector circuit illustrated in FIG. 3B includes a photoelectric conversion element 131b, a transistor 132b, a transistor 133b, a transistor 134b, and a transistor 135.

Note that in the photodetector circuit illustrated in FIG. 3B, the transistor 132b, the transistor 133b, the transistor 134b, and the transistor 135 are field-effect transistors.

The photoelectric conversion element 131b has a first current terminal and a second current terminal, and the voltage Vb is input to the first current terminal of the photoelectric conversion element 131b.

Note that one of the voltage Va and the voltage Vb is the high power supply voltage Vdd, and the other of the voltage Va and the voltage Vb is the low power supply voltage Vss. The high power supply voltage Vdd is a voltage having a relatively higher value than the low power supply voltage Vss, and the low power supply voltage Vss is a voltage having a relatively lower value than the high power supply voltage Vdd. The values of the voltage Va and the voltage Vb may be interchanged depending on the polarity of the transistor, for example. Further, the difference between the voltage Va and the voltage Vb is the power supply voltage.

One of a source and a drain of the transistor 134b is electrically connected to the second current terminal of the photoelectric conversion element 131b, and a light detection control signal is input to a gate of the transistor 134b.

The gate of the transistor 132b is electrically connected to the other of the source and the drain of the transistor 134b.

A photodetection reset signal is input to the gate of the transistor 135, the voltage Va is input to one of the source and the drain of the transistor 135, and the other of the source and the drain of the transistor 135 is the other of the source and the drain of the transistor 134b. Is electrically connected.

An output selection signal is input to the gate of the transistor 133b, and one of the source and the drain of the transistor 133b is electrically connected to one of the source and the drain of the transistor 132b.

Note that the voltage Va is input to the other of the source and the drain of the transistor 132b and the other of the source and the drain of the transistor 133b.

In addition, the photodetector circuit illustrated in FIG. 3B outputs optical data as an optical data signal from the other of the source and the drain of the transistor 132b and the other of the source and the drain of the transistor 133b.

Further, each component of the photodetector circuit illustrated in FIGS. 3A and 3B will be described.

For example, a photodiode or a phototransistor can be used as the photoelectric conversion element 131a and the photoelectric conversion element 131b. In the case of a photodiode, one of the anode and the cathode of the photodiode corresponds to the first current terminal of the photoelectric conversion element, the other of the anode and the cathode of the photodiode corresponds to the second current terminal of the photoelectric conversion element, In the case of a transistor, one of the source and the drain of the phototransistor corresponds to the first current terminal of the photoelectric conversion element, and the other of the source and the drain of the phototransistor corresponds to the second current terminal of the photoelectric conversion element.

The transistors 132a and 132b function as amplification transistors.

The transistors 134a and 134b function as light detection control transistors.

The transistor 135 functions as a light detection reset selection transistor. Note that in the photodetector circuit in this embodiment, the transistor 135 is not necessarily provided; however, by providing the transistor 135, the gate voltage of the transistor 132b can be reset to a desired voltage.

The transistors 133a and 133b function as output selection transistors.

Note that as the transistor 132a, the transistor 132b, the transistor 133a, the transistor 133b, the transistor 134a, the transistor 134b, and the transistor 135, for example, a semiconductor layer in which a channel is formed and a Group 14 semiconductor (such as silicon) in the periodic table is included. Alternatively, a transistor including an oxide semiconductor layer can be used. For example, by using a transistor including the oxide semiconductor layer, variation in gate voltage due to leakage current of the transistor 132a, the transistor 132b, the transistor 133a, the transistor 133b, the transistor 134a, the transistor 134b, and the transistor 135 can be suppressed. it can.

Next, an example of a method for driving the photodetector circuit illustrated in FIGS. 3A and 3B will be described.

First, an example of a method for driving the photodetector circuit illustrated in FIG. 3A will be described with reference to FIG. FIG. 3C is a timing chart for explaining an example of a method for driving the photodetection circuit illustrated in FIG. 3A. The photodetection reset signal, the output selection signal, the photoelectric conversion element 131a, the transistor 133a, and the transistor Each state of 134a is shown. Here, as an example, a case where the photoelectric conversion element 131a is a photodiode will be described.

In the example of the method for driving the photodetector circuit illustrated in FIG. 3A, first, a pulse of the photodetector detection signal is input in a period T31. In addition, a pulse of the light detection control signal is input from the period T31 to the period T32. Note that in the period T31, the input start timing of the light detection reset signal pulse may be earlier than the input start timing of the light detection control signal pulse.

At this time, in the period T31, the photoelectric conversion element 131a is in a state in which current flows in a forward direction (also referred to as a state ST51), the transistor 134a is turned on, and the transistor 133a is turned off.

At this time, the voltage of the gate of the transistor 132a is reset to a constant value.

Next, in a period T32 after the pulse of the light detection reset signal is input, the photoelectric conversion element 131a is in a state where a voltage is applied in the reverse direction (also referred to as a state ST52), and the transistor 133a remains in an off state. It is.

At this time, a photocurrent flows between the first current terminal and the second current terminal of the photoelectric conversion element 131a in accordance with the illuminance of light incident on the photoelectric conversion element 131a. Further, the voltage value of the gate of the transistor 132a changes in accordance with the photocurrent. At this time, the value of the channel resistance between the source and drain of the transistor 132a changes.

Further, in a period T33 after the pulse of the light detection control signal is input, the transistor 134a is turned off.

At this time, the voltage of the gate of the transistor 132a is held at a value corresponding to the photocurrent of the photoelectric conversion element 131a in the period T32. Note that the period T33 is not necessarily provided; however, by providing the period T33, the timing at which the optical data signal is output can be set as appropriate in the photodetector circuit. The timing for outputting the data signal can be set as appropriate.

Next, in a period T34, a pulse of the output selection signal is input.

At this time, the photoelectric conversion element 131a remains in the state ST52, the transistor 133a is turned on, and current flows through the source and drain of the transistor 132a and the source and drain of the transistor 133a. The current flowing through the source and drain of the transistor 132a and the source and drain of the transistor 133a depends on the value of the gate voltage of the transistor 132a. Therefore, the optical data has a value corresponding to the illuminance of light incident on the photoelectric conversion element 131a. Further, the photodetector circuit illustrated in FIG. 3A outputs an optical data signal from the other of the source and the drain of the transistor 132a and the other of the other of the source and the drain of the transistor 133a. The above is the example of the method for driving the photodetector circuit illustrated in FIG.

Next, an example of a method for driving the photodetector circuit illustrated in FIG. 3B will be described with reference to FIG. FIG. 3D is a diagram for describing an example of a method for driving the photodetector circuit illustrated in FIG.

In the example of the method for driving the photodetector circuit illustrated in FIG. 3B, first, a pulse of a light detection reset signal is input in a period T41, and a pulse of a light detection control signal is input from a period T41 to a period T42. Note that in the period T41, the timing for starting the input of the pulse of the light detection reset signal may be earlier than the timing for starting the input of the pulse of the light detection control signal.

At this time, in the period T41, the photoelectric conversion element 131b is in the state ST51 and the transistor 134b is turned on, so that the gate voltage of the transistor 132b is reset to a value equivalent to the voltage Va.

Further, in a period T42 after the pulse of the light detection reset signal is input, the photoelectric conversion element 131b is in the state ST52, the transistor 134b is kept on, and the transistor 135 is turned off.

At this time, a photocurrent flows between the first current terminal and the second current terminal of the photoelectric conversion element 131b in accordance with the illuminance of light incident on the photoelectric conversion element 131b. Further, the voltage value of the gate of the transistor 132b changes according to the photocurrent. At this time, the value of the channel resistance between the source and drain of the transistor 132b changes.

Further, in a period T43 after the pulse of the light detection control signal is input, the transistor 134b is turned off.

At this time, the voltage of the gate of the transistor 132b is held at a value corresponding to the photocurrent of the photoelectric conversion element 131b in the period T42. Note that the period T43 is not necessarily provided; however, by providing the period T43, the timing at which the optical data signal is output can be set as appropriate in the photodetector circuit. The timing for outputting the data signal can be set as appropriate.

Further, in a period T44, a pulse of the output selection signal is input.

At this time, the photoelectric conversion element 131b remains in the state ST52, and the transistor 133b is turned on.

When the transistor 133b is turned on, the photodetector circuit in FIG. 3B outputs an optical data signal from the other of the source and the drain of the transistor 132b and the other of the source and the drain of the transistor 133b. The current flowing through the source and drain of the transistor 132b and the source and drain of the transistor 133b depends on the value of the gate voltage of the transistor 132b. Therefore, the optical data has a value corresponding to the illuminance of light incident on the photoelectric conversion element 131b. The above is the example of the method for driving the photodetector circuit illustrated in FIG.

As described with reference to FIGS. 3A to 3D, an example of the light detection circuit in this embodiment includes a photoelectric conversion element, a light detection control transistor, and an amplification transistor, and includes a light detection control signal. The optical data is generated according to the above, and the optical data is output as the data signal according to the output selection signal. With the above configuration, optical data can be generated and output by the photodetection circuit.

(Embodiment 4)
In this embodiment, an example of a display circuit in the input / output device of the above embodiment is described.

Examples of the display circuit in this embodiment will be described with reference to FIGS. FIG. 4 is a diagram for describing an example of the display circuit in this embodiment.

First, structural examples of the display circuit in this embodiment will be described with reference to FIGS. 4A and 4B are diagrams each illustrating an example of a structure of the display circuit in this embodiment.

The display circuit illustrated in FIG. 4A includes a transistor 151a, a liquid crystal element 152a, and a capacitor 153a.

Note that in the display circuit illustrated in FIG. 4A, the transistor 151a is a field-effect transistor.

In the input / output device, the liquid crystal element includes a first display electrode, a second display electrode, and a liquid crystal layer. The light transmittance of the liquid crystal layer changes according to the voltage applied between the first display electrode and the second display electrode.

In the input / output device, the capacitor includes a first capacitor electrode, a second capacitor electrode, and a dielectric layer overlapping with the first capacitor electrode and the second capacitor electrode. The capacitor accumulates electric charge according to a voltage applied between the first capacitor electrode and the second capacitor electrode.

A display data signal is input to one of a source and a drain of the transistor 151a, and a display selection signal is input to a gate of the transistor 151a.

The first display electrode of the liquid crystal element 152a is electrically connected to the other of the source and the drain of the transistor 151a, and the voltage Vc is input to the second display electrode of the liquid crystal element 152a. The value of the voltage Vc can be set as appropriate.

The first capacitor electrode of the capacitor 153a is electrically connected to the other of the source and the drain of the transistor 151a, and the voltage Vc is input to the second capacitor electrode of the capacitor 153a.

The display circuit illustrated in FIG. 4B includes a transistor 151b, a liquid crystal element 152b, a capacitor 153b, a capacitor 154, a transistor 155, and a transistor 156.

Note that in the display circuit illustrated in FIG. 4B, the transistor 151b, the transistor 155, and the transistor 156 are field-effect transistors.

A display data signal is input to one of a source and a drain of the transistor 155, and a write selection signal (also referred to as a signal WSEL) that is a pulse signal is input to the gate of the transistor 155. The write selection signal can be generated, for example, by outputting a pulse signal from the shift register by a circuit including the shift register.

The first capacitor electrode of the capacitor 154 is electrically connected to the other of the source and the drain of the transistor 155, and the voltage Vc is input to the second capacitor electrode of the capacitor 154.

One of a source and a drain of the transistor 151b is electrically connected to the other of the source and the drain of the transistor 155, and a display selection signal is input to a gate of the transistor 151b.

The first display electrode of the liquid crystal element 152b is electrically connected to the other of the source and the drain of the transistor 151b, and the voltage Vc is input to the second display electrode of the liquid crystal element 152b.

The first capacitor electrode of the capacitor 153b is electrically connected to the other of the source and the drain of the transistor 151b, and the voltage Vc is input to the second capacitor electrode of the capacitor 153b. The value of the voltage Vc is appropriately set according to the specifications of the display circuit.

A reference voltage is input to one of a source and a drain of the transistor 156, the other of the source and the drain of the transistor 156 is electrically connected to the other of the source and the drain of the transistor 151b, and the gate of the transistor 156 is connected to the gate of the transistor 156. A display reset signal (also referred to as a signal DRST) which is a pulse signal is input.

Further, each component of the display circuit illustrated in FIGS. 4A and 4B will be described.

The transistors 151a and 151b function as display selection transistors.

As the liquid crystal layer in the liquid crystal element 152a and the liquid crystal element 152b, a liquid crystal layer that transmits light when a voltage applied to the first display electrode and the second display electrode is 0 V can be used. A refractive liquid crystal (also referred to as an ECB liquid crystal), a liquid crystal to which a dichroic dye is added (also referred to as a GH liquid crystal), a polymer dispersed liquid crystal, a liquid crystal layer including a discotic liquid crystal, or the like can be used. A liquid crystal layer exhibiting a blue phase may be used as the liquid crystal layer. The liquid crystal layer exhibiting a blue phase is composed of, for example, a liquid crystal composition including a liquid crystal exhibiting a blue phase and a chiral agent. A liquid crystal exhibiting a blue phase has a response speed as short as 1 msec or less and is optically isotropic. Therefore, alignment treatment is unnecessary and viewing angle dependency is small. Therefore, the operation speed can be improved by using a liquid crystal exhibiting a blue phase. For example, since the field sequential input / output device in the above embodiment requires a higher operating speed than a display device using a color filter, the liquid crystal element in the field sequential input / output device in the above embodiment is used. It is preferable to use a liquid crystal exhibiting the above blue phase.

The capacitor 153a and the capacitor 153b function as a storage capacitor in which a voltage having a value corresponding to a display data signal is applied between the first capacitor electrode and the second capacitor electrode in accordance with the transistor 151a or the transistor 151b. Although the capacitor 153a and the capacitor 153b are not necessarily provided, the provision of the capacitor 153a and the capacitor 153b suppresses fluctuations in the voltage applied to the liquid crystal element due to the leakage current of the display selection transistor. Can do.

The capacitor 154 functions as a storage capacitor in which a voltage corresponding to a display data signal is applied between the first capacitor electrode and the second capacitor electrode in accordance with the transistor 155.

The transistor 155 functions as a write selection transistor that selects whether to input a display data signal to the capacitor 154.

The transistor 156 functions as a display reset selection transistor that selects whether to reset the voltage applied to the liquid crystal element 152b.

Note that as the transistor 151a, the transistor 151b, the transistor 155, and the transistor 156, for example, a transistor in which a channel is formed and a semiconductor layer or an oxide semiconductor layer including a Group 14 semiconductor (such as silicon) in the periodic table is included. Can be used.

Next, an example of a method for driving the display circuit illustrated in FIGS. 4A and 4B is described.

First, an example of a method for driving the display circuit illustrated in FIG. 4A will be described with reference to FIG. FIG. 4C is a timing chart for explaining an example of a method for driving the display circuit illustrated in FIG. 4A, and shows respective states of the display data signal and the display selection signal.

In the example of the method for driving the display circuit illustrated in FIG. 4A, when the pulse of the display selection signal is input, the transistor 151a is turned on.

When the transistor 151a is turned on, a display data signal is input to the display circuit, and the voltages of the first display electrode of the liquid crystal element 152a and the first capacitor electrode of the capacitor 153a are equal to the voltage of the display data signal. Become.

At this time, the liquid crystal element 152a is in a writing state (also referred to as a state wt) and has a light transmittance according to the display data signal, so that it corresponds to the data of the display data signal (data D11 to data DX). Display.

After that, the transistor 151a is turned off, the liquid crystal element 152a is in a holding state (also referred to as a state hld), and a voltage applied between the first display electrode and the second display electrode is next selected for display. Until the signal pulse is input, the fluctuation amount from the initial value is held so as not to be larger than the reference value. When the liquid crystal element 152a is in the holding state, the light unit in the input / output device of the above embodiment is in a lighting state.

Next, an example of a method for driving the display circuit illustrated in FIG. 4B will be described with reference to FIG. FIG. 4D is a timing chart for describing an example of a method for driving the display circuit illustrated in FIG.

In the example of the method for driving the display circuit illustrated in FIG. 4B, when a pulse of a display reset signal is input, the transistor 156 is turned on, and the first display electrode of the liquid crystal element 152b and the first of the capacitor 153b are turned on. The voltage of the capacitor electrode is reset to a reference voltage.

In addition, when a pulse of the write selection signal is input, the transistor 155 is turned on, the display data signal is input to the display circuit, and the voltage of the first capacitor electrode of the capacitor 154 is equal to the voltage of the display data signal. Value.

After that, when a pulse of the display selection signal is input, the transistor 151b is turned on, and the voltage of the first display electrode of the liquid crystal element 152b and the first capacitor electrode of the capacitor 153b is changed to the first voltage of the capacitor 154. The value is equivalent to the voltage of the capacitive electrode.

At this time, the liquid crystal element 152b is in a writing state and has a light transmittance corresponding to the display data signal, whereby the display circuit is in a display state corresponding to the data of the display data signal (data D11 to data DX). become.

After that, the transistor 151b is turned off, the liquid crystal element 152b is in a holding state, a voltage applied between the first display electrode and the second display electrode, and then a pulse of a display selection signal are input. Until the fluctuation amount from the initial value does not become larger than the reference value. When the liquid crystal element 152b is in the holding state, the light unit in the input / output device of the above embodiment is in a lighting state.

As described with reference to FIGS. 4A and 4B, an example of the display circuit in this embodiment includes a display selection transistor and a liquid crystal element. With the above structure, the display circuit can be brought into a display state corresponding to the display data signal.

In addition, as described with reference to FIG. 4B, an example of the display circuit in this embodiment includes a write selection transistor and a capacitor in addition to the display selection transistor and the liquid crystal element. With the above structure, while the liquid crystal element is set to a display state corresponding to the data of a certain display data signal, data of the next display data signal can be written to the capacitor element. Therefore, the operation speed of the display circuit can be improved.

(Embodiment 5)
In the present embodiment, an example of the second light unit in the input / output device of the first embodiment will be described.

A structural example of the light unit in this embodiment will be described with reference to FIG. FIG. 5 is a schematic diagram showing a configuration example of the light unit in the present embodiment.

The light unit shown in FIG. 5 includes a light source 201, a light guide plate 202, and a fixing material 203. 5 overlaps with a light detection circuit of a pixel portion (also referred to as PX) 205. The light unit illustrated in FIG.

As the light source 201, as shown in Embodiment Mode 1, a light-emitting diode that emits light in the visible light region can be used.

The fixing member 203 has a function of fixing the light source 201 and the light guide plate 202. As the fixing material 203, a light-shielding material is preferably used. By using a light-shielding material as the fixing material 203, leakage of light emitted from the light source 201 to the outside can be suppressed. Note that the fixing member 203 is not necessarily provided.

The light unit shown in FIG. 5 makes light from the light source 201 incident on the light guide plate 202. For example, when the object to be read is not in contact with the light guide plate 202, the light from the light source 201 is totally reflected in the light guide plate 202. In addition, when an object to be read such as a finger 204 is in contact with the light guide plate 202, light from the light source 201 is scattered at a contact portion between the finger 204 and the light guide plate 202 and enters the light detection circuit.

In addition, the light unit illustrated in FIG. 5 may be switched between a lighting state and a light-off state by including a light control circuit.

As described with reference to FIG. 5, an example of the light unit in the present embodiment includes a light source and a light guide plate, totally reflects light from the light source in the light guide plate, and an object to be read contacts the light guide plate. In this case, the reflected light of the object to be read enters the light detection circuit at the contact portion. With the above structure, the influence of light in an environment where the input / output device is placed can be suppressed.

(Embodiment 6)
In this embodiment, a transistor that can be used as a transistor in the input / output device described in the above embodiment is described.

In the input / output device described using the above embodiment, a transistor includes, for example, a channel formed and a semiconductor layer or an oxide semiconductor layer containing a Group 14 semiconductor (such as silicon) in the periodic table Can be used. Note that a layer in which a channel is formed is also referred to as a channel formation layer.

Note that the semiconductor layer may be a single crystal semiconductor layer, a polycrystalline semiconductor layer, a microcrystalline semiconductor layer, or an amorphous semiconductor layer.

Further, in the input / output device described using the above embodiment, a transistor including an oxide semiconductor layer that can be used as a transistor can be intrinsic (also referred to as an I-type) or substantially, for example, by being highly purified. A transistor having an intrinsic oxide semiconductor layer can be used. Purifying is a concept including eliminating hydrogen in an oxide semiconductor layer as much as possible and reducing defects due to oxygen deficiency in the oxide semiconductor layer by supplying oxygen to the oxide semiconductor layer. is there.

An example of a structure of the transistor including the oxide semiconductor layer will be described with reference to FIGS. FIG. 6 is a schematic cross-sectional view illustrating a structural example of a transistor in this embodiment.

The transistor illustrated in FIG. 6A is one of bottom-gate transistors and is also referred to as an inverted staggered transistor.

The transistor illustrated in FIG. 6A includes a conductive layer 401a, an insulating layer 402a, an oxide semiconductor layer 403a, a conductive layer 405a, and a conductive layer 406a.

The conductive layer 401a is provided over the substrate 400a, the insulating layer 402a is provided over the conductive layer 401a, and the oxide semiconductor layer 403a overlaps with the conductive layer 401a through the insulating layer 402a, so that the conductive layer 405a The conductive layer 406a is provided over part of the oxide semiconductor layer 403a.

Further, in FIG. 6A, part of the upper surface of the oxide semiconductor layer 403a of the transistor (a portion where the conductive layer 405a and the conductive layer 406a are not provided on the upper surface) is in contact with the oxide insulating layer 407a.

The transistor illustrated in FIG. 6B is a channel protection transistor (also referred to as a channel stop transistor) that is one of bottom-gate structures, and is also referred to as an inverted staggered transistor.

A transistor illustrated in FIG. 6B includes a conductive layer 401b, an insulating layer 402b, an oxide semiconductor layer 403b, a conductive layer 405b, a conductive layer 406b, and an oxide insulating layer 407b.

The conductive layer 401b is provided over the substrate 400b, the insulating layer 402b is provided over the conductive layer 401b, and the oxide semiconductor layer 403b overlaps with the conductive layer 401b with the insulating layer 402b interposed therebetween. The layer 407b is provided over the oxide semiconductor layer 403b, and the conductive layer 405b and the conductive layer 406b are provided over part of the oxide semiconductor layer 403b with the oxide insulating layer 407b provided therebetween.

The transistor illustrated in FIG. 6C is one of bottom-gate transistors.

A transistor illustrated in FIG. 6C includes a conductive layer 401c, an insulating layer 402c, an oxide semiconductor layer 403c, a conductive layer 405c, and a conductive layer 406c.

The conductive layer 401c is provided over the substrate 400c, the insulating layer 402c is provided over the conductive layer 401c, and the conductive layer 405c and the conductive layer 406c are provided over part of the insulating layer 402c. The semiconductor layer 403c overlaps with the conductive layer 401c with the insulating layer 402c interposed therebetween.

Further, in FIG. 6C, the top surface and the side surface of the oxide semiconductor layer 403c in the transistor are in contact with the oxide insulating layer 407c.

Note that in FIGS. 6A to 6C, a protective insulating layer may be provided over the oxide insulating layer.

The transistor illustrated in FIG. 6D is one of top-gate transistors.

A transistor illustrated in FIG. 6D includes a conductive layer 401d, an insulating layer 402d, an oxide semiconductor layer 403d, a conductive layer 405d, and a conductive layer 406d.

The oxide semiconductor layer 403d is provided over the substrate 400d with the insulating layer 447 provided therebetween. The conductive layer 405d and the conductive layer 406d are provided over the oxide semiconductor layer 403d, respectively. The conductive layer 401d is provided over the layer 403d, the conductive layer 405d, and the conductive layer 406d, and overlaps with the oxide semiconductor layer 403d with the insulating layer 402d provided therebetween.

Further, each component illustrated in FIGS. 6A to 6D will be described.

As the substrates 400a to 400d, for example, a light-transmitting substrate can be used. As the light-transmitting substrate, for example, a glass substrate or a plastic substrate can be used.

The insulating layer 447 functions as a base layer for preventing diffusion of an impurity element from the substrate 400d.

As the insulating layer 447, for example, a silicon nitride layer, a silicon oxide layer, a silicon nitride oxide layer, a silicon oxynitride layer, an aluminum oxide layer, or an aluminum oxynitride layer can be used. Alternatively, the insulating layer 447 can be a stack of materials that can be used for the insulating layer 447.

Each of the conductive layers 401a to 401d functions as a gate of the transistor. Note that a layer functioning as a gate of a transistor is also referred to as a gate electrode or a gate wiring.

Note that the transistor in this embodiment includes a conductive layer which overlaps with a conductive layer serving as a gate through an oxide semiconductor layer in addition to the components of the transistors illustrated in FIGS. 6A to 6D. It may be. The conductive layer also functions as a gate of the transistor. With the above structure, the threshold voltage of the transistor can be controlled and incidence of light on the oxide semiconductor layer can be suppressed.

As the conductive layers 401a to 401d, a layer of a metal material such as molybdenum, titanium, chromium, tantalum, tungsten, aluminum, copper, neodymium, or scandium, or an alloy material containing any of these materials as its main component can be used. . Alternatively, the conductive layers 401a to 401d can be a stack of materials that can be used for forming the conductive layers 401a to 401d.

Each of the insulating layers 402a to 402d functions as a gate insulating layer of the transistor. Note that a layer functioning as a gate insulating layer of a transistor is also referred to as a gate insulating layer.

As the insulating layers 402a to 402c, for example, a silicon oxide layer, a silicon nitride layer, a silicon oxynitride layer, a silicon nitride oxide layer, an aluminum oxide layer, an aluminum nitride layer, an aluminum oxynitride layer, an aluminum nitride oxide layer, or hafnium oxide Layers can be used. Alternatively, the insulating layers 402a to 402c can be a stack of materials that can be used for the insulating layers 402a to 402c. As the insulating layer 402d, an oxide insulating layer can be used, for example, a silicon oxide layer can be used.

Each of the oxide semiconductor layers 403a to 403d functions as a layer in which a channel of the transistor is formed. An oxide semiconductor that can be used for the oxide semiconductor layers 403a to 403d contains at least one element selected from In, Ga, Sn, Zn, Al, Mg, Hf, and a lanthanoid. For example, a quaternary metal oxide, a ternary metal oxide, a binary metal oxide, or the like can be used. As the quaternary metal oxide, for example, an In—Sn—Ga—Zn—O-based metal oxide or the like can be used. As the ternary metal oxide, for example, an In—Ga—Zn—O metal oxide, an In—Sn—Zn—O metal oxide, an In—Al—Zn—O metal oxide, a Sn—Ga— Zn-O metal oxide, Al-Ga-Zn-O metal oxide, Sn-Al-Zn-O metal oxide, In-Hf-Zn-O metal oxide, In-La-Zn- O-based metal oxide, In-Ce-Zn-O-based metal oxide, In-Pr-Zn-O-based metal oxide, In-Nd-Zn-O-based metal oxide, In-Pm-Zn-O-based Metal oxide, In-Sm-Zn-O-based metal oxide, In-Eu-Zn-O-based metal oxide, In-Gd-Zn-O-based metal oxide, In-Tb-Zn-O-based metal oxide , In-Dy-Zn-O-based metal oxide, In-Ho-Zn-O-based metal oxide, In-Er-Zn-O-based Genus oxide, In-Tm-Zn-O-based metal oxide, In-Yb-Zn-O-based metal oxide, or In-Lu-Zn-O-based or the like can be used metal oxides. Examples of the binary metal oxide include In-Zn-O metal oxide, Sn-Zn-O metal oxide, Al-Zn-O metal oxide, Zn-Mg-O metal oxide, An Sn—Mg—O-based metal oxide, an In—Mg—O-based metal oxide, an In—Sn—O-based metal oxide, an In—Ga—O-based metal oxide, or the like can be used. As the oxide semiconductor, for example, an In—O based metal oxide, a Sn—O based metal oxide, a Zn—O based metal oxide, or the like can be used. The metal oxide that can be used as the oxide semiconductor may contain silicon oxide.

In the case of using an In—Zn—O-based metal oxide, for example, In: Zn = 50: 1 to In: Zn = 1: 2 (in terms of molar ratio, In ₂ O ₃ : ZnO = 25: 1 to In ₂ O ₃ : ZnO = 1: 4), preferably In: Zn = 20: 1 to In: Zn = 1: 1 (in terms of molar ratio, In ₂ O ₃ : ZnO = 10: 1 to In ₂ O ₃ : ZnO = 1: 2), more preferably In: Zn = 15: 1 to In: Zn = 1.5: 1 (in terms of mole ratio, In ₂ O ₃ : ZnO = 15: 2 to In ₂ O ₃ : An In—Zn—O-based metal oxide semiconductor layer can be formed using an oxide target having a composition ratio of ZnO = 3: 4). For example, a target used for forming an In—Zn—O-based oxide semiconductor has R> 1.5P + Q when the atomic ratio is In: Zn: O = P: Q: R. By increasing the amount of In, the mobility of the transistor can be improved.

For the oxide semiconductor, a material represented by InMO ₃ (ZnO) _m (m is larger than 0) can also be used. M in InMO ₃ (ZnO) _m represents one or more metal elements selected from Ga, Al, Mn, and Co.

Each of the conductive layers 405a to 405d and the conductive layers 406a to 406d functions as a source or a drain of the transistor. Note that a layer functioning as the source of the transistor is also referred to as a source electrode or a source wiring, and a layer functioning as the drain of the transistor is also referred to as a drain electrode or a drain wiring.

As the conductive layers 405a to 405d and the conductive layers 406a to 406d, for example, a metal material such as aluminum, chromium, copper, tantalum, titanium, molybdenum, or tungsten, or an alloy material containing any of these metal materials as a main component Layers can be used. Alternatively, each of the conductive layers 405a to 405d and the conductive layers 406a to 406d can be a stack of materials that can be used for the conductive layers 405a to 405d and the conductive layers 406a to 406d. .

Alternatively, the conductive layers 405a to 405d and the conductive layers 406a to 406d can be formed using a layer containing a conductive metal oxide. As the conductive metal oxide, for example, indium oxide, tin oxide, zinc oxide, an indium tin oxide alloy, or an indium zinc oxide alloy can be used. Note that the conductive metal oxide which can be used for the conductive layers 405a to 405d and the conductive layers 406a to 406d may contain silicon oxide.

As the oxide insulating layers 407a to 407c, for example, a silicon oxide layer or the like can be used. Note that the oxide insulating layer 407b functions as a layer for protecting a channel formation layer of the transistor (also referred to as a channel protective layer).

Note that as illustrated in FIGS. 6A to 6D, the transistor in this embodiment does not necessarily have a structure in which the entire oxide semiconductor layer overlaps with a conductive layer functioning as a gate electrode. However, by using a structure in which the entire oxide semiconductor layer overlaps with the conductive layer functioning as the gate electrode, incidence of light on the oxide semiconductor layer can be suppressed.

Further, as an example of a method for manufacturing the transistor in this embodiment, an example of a method for manufacturing the transistor illustrated in FIG. 6A will be described with reference to FIGS. 7A to 7E are schematic cross-sectional views for describing an example of a method for manufacturing the transistor illustrated in FIG.

First, as shown in FIG. 7A, a substrate 400a is prepared, a first conductive film is formed over the substrate 400a, and a part of the first conductive film is etched to form a conductive layer 401a. To do.

For example, the first conductive film can be formed by forming a film of a material that can be used for the conductive layer 401a by a sputtering method. Alternatively, the first conductive film can be formed by stacking films of materials applicable to the conductive layer 401a.

Note that by using a high-purity gas from which impurities such as hydrogen, water, a hydroxyl group, or hydride are removed as the sputtering gas, the impurity concentration of the formed film can be reduced.

Note that before the film is formed by a sputtering method, preheating treatment may be performed in a preheating chamber of a sputtering apparatus. By performing the preheating treatment, impurities such as hydrogen and moisture can be eliminated.

Further, before forming a film using a sputtering method, for example, in an argon, nitrogen, helium, or oxygen atmosphere, a voltage is applied to the substrate side using an RF power source without applying a voltage to the target side, You may perform the process (it is also called reverse sputtering) which forms a plasma and modify | reforms a to-be-formed surface. By performing reverse sputtering, powdery substances (also referred to as particles or dust) attached to the formation surface can be removed.

In the case where a film is formed by a sputtering method, residual moisture in the deposition chamber in which the film is formed can be removed using an adsorption-type vacuum pump or the like. As an adsorption-type vacuum pump, for example, a cryopump, an ion pump, a titanium sublimation pump, or the like can be used. Further, residual moisture in the deposition chamber can be removed using a turbo pump provided with a cold trap.

Further, for example, the conductive layer 401a can be formed by forming a resist mask over part of the first conductive film by a photolithography process and etching the first conductive film using the resist mask. In this case, the resist mask is removed after the conductive layer 401a is formed.

Further, a resist mask may be formed using an inkjet method. By using the ink jet method, a photomask is not necessary, so that manufacturing cost can be reduced. Alternatively, a resist mask may be formed using an exposure mask having a plurality of regions with different transmittances (also referred to as a multi-tone mask). By using a multi-tone mask, a resist mask having regions with different thicknesses can be formed, so that the number of resist masks used for manufacturing a transistor can be reduced.

Next, as illustrated in FIG. 7B, the insulating layer 402a is formed by forming a first insulating film over the conductive layer 401a.

For example, the first insulating film can be formed by forming a film of a material that can be used for the insulating layer 402a by a sputtering method, a plasma CVD method, or the like. Alternatively, the first insulating film can be formed by stacking films of materials that can be used for the insulating layer 402a. Further, by forming a film of a material that can be used for the insulating layer 402a by using a high-density plasma CVD method (for example, a high-density plasma CVD method using μ waves (for example, μ waves having a frequency of 2.45 GHz)), The insulating layer 402a can be made dense and the withstand voltage of the insulating layer 402a can be improved.

Next, as illustrated in FIG. 7C, an oxide semiconductor film is formed over the insulating layer 402a, and then part of the oxide semiconductor film is etched, whereby the oxide semiconductor layer 403a is formed.

For example, the oxide semiconductor film can be formed by forming a film of an oxide semiconductor material that can be used for the oxide semiconductor layer 403a by a sputtering method. Note that the oxide semiconductor film may be formed in a rare gas atmosphere, an oxygen atmosphere, or a mixed atmosphere of a rare gas and oxygen.

An oxide semiconductor film can be formed using an oxide target having a composition ratio of In ₂ O ₃ : Ga ₂ O ₃ : ZnO = 1: 1: 1 [molar ratio] as a sputtering target. For example, the oxide semiconductor film may be formed using an oxide target having a composition ratio of In ₂ O ₃ : Ga ₂ O ₃ : ZnO = 1: 1: 2 [molar ratio].

Further, when the oxide semiconductor film is formed by a sputtering method, the substrate 400a may be in a reduced pressure state, and the substrate 400a may be heated to 100 ° C to 600 ° C, preferably 200 ° C to 400 ° C. By heating the substrate 400a, the impurity concentration of the oxide semiconductor film can be reduced, and damage to the oxide semiconductor film due to a sputtering method can be reduced.

Further, for example, the oxide semiconductor layer 403a can be formed by forming a resist mask over part of the oxide semiconductor film by a photolithography step and etching the oxide semiconductor film using the resist mask. . Note that in this case, the resist mask is removed after the oxide semiconductor film is etched.

Next, as illustrated in FIG. 7D, a second conductive film is formed over the insulating layer 402a and the oxide semiconductor layer 403a, and part of the second conductive film is etched, whereby the conductive layer 405a is formed. Then, a conductive layer 406a is formed.

For example, the second conductive film can be formed by forming a film of a material that can be used for the conductive layers 405a and 406a by a sputtering method or the like. Alternatively, the second conductive film can be formed by stacking films of materials applicable to the conductive layers 405a and 406a.

Further, for example, a resist mask is formed over part of the second conductive film by a photolithography process, and the conductive film 405a and the conductive layer 406a are formed by etching the second conductive film using the resist mask. be able to. Note that in this case, the resist mask is removed after the conductive layer 405a and the conductive layer 406a are formed.

Next, as illustrated in FIG. 7E, an oxide insulating layer 407a is formed so as to be in contact with the oxide semiconductor layer 403a.

For example, by forming a film that can be used for the oxide insulating layer 407a by a sputtering method in a rare gas (typically argon) atmosphere, an oxygen atmosphere, or a mixed atmosphere of a rare gas and oxygen, The oxide insulating layer 407a can be formed. By forming the oxide insulating layer 407a by a sputtering method, reduction in resistance of the oxide semiconductor layer 403a functioning as a back channel of the transistor can be suppressed. The substrate temperature when the oxide insulating layer 407a is formed is preferably room temperature or higher and 300 ° C. or lower.

Further, before the oxide insulating layer 407a is formed, plasma treatment using a gas such as N ₂ O, N ₂ , or Ar is performed, and adsorbed water or the like attached to the surface of the exposed oxide semiconductor layer 403a is removed. It may be removed. In the case where plasma treatment is performed, the oxide insulating layer 407a is preferably formed without being exposed to the air thereafter.

Further, in the example of the method for manufacturing the transistor illustrated in FIG. 6A, heat treatment is performed at a temperature of, for example, 400 ° C. to 750 ° C., or 400 ° C. to less than the strain point of the substrate. For example, after an oxide semiconductor film is formed, a part of the oxide semiconductor film is etched, a second conductive film is formed, a part of the second conductive film is etched, or an oxide insulating film After the layer 407a is formed, the heat treatment is performed.

Note that as the heat treatment apparatus for performing the above heat treatment, an apparatus for heating an object to be processed by heat conduction or heat radiation from a heating element such as an electric furnace or a resistance heating element can be used, for example, GRTA (Gas Rapid) An RTA (Rapid Thermal Annealing) apparatus such as a Thermal Annealing (RTA) apparatus or an LRTA (Lamp Rapid Thermal Annealing) apparatus can be used. The LRTA apparatus is an apparatus that heats an object to be processed by radiation of light (electromagnetic waves) emitted from a lamp such as a halogen lamp, a metal halide lamp, a xenon arc lamp, a carbon arc lamp, a high pressure sodium lamp, or a high pressure mercury lamp. A GRTA apparatus is an apparatus that performs heat treatment using a high-temperature gas. As the high-temperature gas, for example, a rare gas or an inert gas (for example, nitrogen) that does not react with an object to be processed by heat treatment can be used.

In addition, after the heat treatment, while maintaining the heating temperature or in the process of lowering the temperature from the heating temperature, a high purity oxygen gas, a high purity N ₂ O is added to the same furnace as the heat treatment. Gas or ultra-dry air (an atmosphere having a dew point of −40 ° C. or lower, preferably −60 ° C. or lower) may be introduced. At this time, the oxygen gas or the N _{2 O} gas, water, preferably contains no hydrogen, and the like. Further, the purity of the oxygen gas or N ₂ O gas introduced into the heat treatment apparatus is 6 N or more, preferably 7 N or more, that is, the impurity concentration in the oxygen gas or N ₂ O gas is 1 ppm or less, preferably 0.1 ppm or less. It is preferable that Oxygen is supplied to the oxide semiconductor layer 403a by the action of oxygen gas or N ₂ O gas, so that the oxide semiconductor layer 403a can be highly purified.

Further, separately from the heat treatment, after the oxide insulating layer 407a is formed, heat treatment is performed in an inert gas atmosphere or an oxygen gas atmosphere (preferably 200 ° C. to 400 ° C., for example, 250 ° C. to 350 ° C. ) May be performed.

Alternatively, oxygen doping treatment with oxygen plasma may be performed after the insulating layer 402a is formed, the oxide semiconductor film is formed, the conductive layer to be the source electrode or the drain electrode is formed, the oxide insulating layer is formed, or after the heat treatment. For example, the oxygen doping process may be performed with a high-density plasma of 2.45 GHz. By performing the oxygen doping treatment, variation in electric characteristics of the manufactured transistor can be reduced.

Through the above process, impurities such as hydrogen, moisture, a hydroxyl group, or a hydride (also referred to as a hydrogen compound) are excluded from the oxide semiconductor layer 403a and oxygen is supplied to the oxide semiconductor layer 403a, whereby oxygen gas Alternatively, defects due to oxygen deficiency in the oxide semiconductor layer 403a can be reduced by the action of the N ₂ O gas.

Note that although an example of a method for manufacturing the transistor illustrated in FIG. 6A is described, the present invention is not limited to this, and for example, each component illustrated in FIGS. 6B to 6D has a name illustrated in FIG. ) And at least part of the functions are the same as those of each component illustrated in FIG. 6A, the description of the example of the method for manufacturing the transistor illustrated in FIG. can do.

As described with reference to FIGS. 6 and 7, an example of the transistor in this embodiment includes a conductive layer having a function as a gate, an insulating layer having a function as a gate insulating layer, and a gate insulating layer. An oxide semiconductor layer which overlaps with a conductive layer having a function as a gate through a functional insulating layer and is electrically connected to the oxide semiconductor layer and functions as one of a source and a drain And a conductive layer that is electrically connected to the oxide semiconductor layer and functions as the other of the source and the drain.

An oxide semiconductor layer in which a channel is formed is an oxide semiconductor layer that is i-type or substantially i-type by being highly purified. By highly purifying the oxide semiconductor layer, the carrier concentration of the oxide semiconductor layer is less than 1 × 10 ¹⁴ / cm ³ , preferably less than 1 × 10 ¹² / cm ³ , and more preferably 1 × 10 ¹¹ / cm ^3. It is possible to suppress the change in characteristics due to a temperature change. Further, with the above structure, the off current per channel width of 1 μm is set to 10 aA (1 × 10 ⁻¹⁷ A) or less, and further the off current per channel width of 1 μm is 1 aA (1 × 10 ⁻¹⁸ A). Hereinafter, the off current per channel width of 1 μm is 10 zA (1 × 10 ⁻²⁰ A) or less, further the off current per channel width of 1 μm is 1 zA (1 × 10 ⁻²¹ A) or less, and further per 1 μm of channel width. The off current can be made 100yA (1 × 10 ⁻²² A) or less. The lower the off-state current of the transistor, the better. However, the lower limit value of the off-state current of the transistor in this embodiment is estimated to be about 10 ⁻³⁰ A / μm.

Further, an example of calculating the value of off-state current in an example of a transistor including an oxide semiconductor layer in this embodiment, using leakage current measurement by a circuit for characteristic evaluation will be described.

The leakage current measurement by the characteristic evaluation circuit will be described with reference to FIG. FIG. 8 is a diagram for explaining the characteristic evaluation circuit.

First, a circuit configuration of the characteristic evaluation circuit will be described with reference to FIG. FIG. 8A is a circuit diagram illustrating a circuit configuration of the characteristic evaluation circuit.

The characteristic evaluation circuit illustrated in FIG. 8A includes a plurality of measurement systems 801. The plurality of measurement systems 801 are connected in parallel to each other. Here, as an example, eight measurement systems 801 are connected in parallel. By using a plurality of measurement systems 801, a plurality of measurements can be performed simultaneously.

The measurement system 801 includes a transistor 811, a transistor 812, a capacitor 813, a transistor 814, and a transistor 815.

The voltage V <b> 1 is input to one of a source and a drain of the transistor 811, and a voltage Vext_a is input to the gate of the transistor 811. The transistor 811 is a charge injection transistor.

One of a source and a drain of the transistor 812 is connected to the other of the source and the drain of the transistor 811, the voltage V2 is input to the other of the source and the drain of the transistor 812, and a voltage Vext_b is input to the gate of the transistor 812. Is done. The transistor 812 is a transistor for evaluating leakage current. Note that the leakage current here is a leakage current including an off-state current of the transistor.

The first capacitor electrode of the capacitor 813 is connected to the other of the source and the drain of the transistor 811, and the voltage V <b> 2 is input to the second capacitor electrode of the capacitor 813. Here, the voltage V2 is 0V.

A voltage V3 is input to one of a source and a drain of the transistor 814, and a gate of the transistor 814 is connected to the other of the source and the drain of the transistor 811. Note that a connection portion between the gate of the transistor 814 and the other of the source and the drain of the transistor 811, one of the source and the drain of the transistor 812, and the first capacitor electrode of the capacitor 813 is also referred to as a node A. Here, the voltage V3 is 5V.

One of a source and a drain of the transistor 815 is connected to the other of the source and the drain of the transistor 814, the voltage V4 is input to the other of the source and the drain of the transistor 815, and a voltage Vext_c is input to the gate of the transistor 815. Is done. Here, the voltage Vext_c is 0.5V.

Further, the measurement system 801 outputs a voltage at a connection point between the other of the source and the drain of the transistor 814 and one of the source and the drain of the transistor 815 as the output voltage Vout.

Here, as an example of the transistor 811, a transistor including an oxide semiconductor layer and having a channel length L = 10 μm and a channel width W = 10 μm is used. As an example of the transistor 814 and the transistor 815, a transistor including an oxide semiconductor layer and having a channel length L = 3 μm and a channel width W = 100 μm is used. Further, as an example of the transistor 812, an oxide semiconductor layer is included, a source electrode and a drain electrode are in contact with an upper portion of the oxide semiconductor layer, an overlap region between the source electrode, the drain electrode, and the gate electrode is not provided, and the width is 1 μm. A bottom-gate transistor having a certain offset region is used. By providing the offset region, parasitic capacitance can be reduced. Further, a sample of six transistors (also referred to as SMP) having different channel lengths L and channel widths W is used as the transistor 812 (see Table 1).

As shown in FIG. 8A, by separately providing a charge injection transistor and a leakage current evaluation transistor, the leakage current evaluation transistor is always kept off during charge injection. Can do. When a charge injection transistor is not provided, it is necessary to turn on the leakage current evaluation transistor once at the time of charge injection, but it takes time to reach the steady state from the on state to the off state. In such an element, measurement takes time.

Further, by separately providing a charge injection transistor and a leakage current evaluation transistor, each transistor can be appropriately sized. Further, by making the channel width W of the leakage current evaluation transistor larger than the channel width W of the charge injection transistor, the leakage current component of the characteristic evaluation circuit other than the leakage current of the leakage current evaluation transistor is relatively Can be small. As a result, the leakage current of the leakage current evaluation transistor can be measured with high accuracy. At the same time, since it is not necessary to turn on the leakage current evaluation transistor once in charge injection, there is no influence of voltage fluctuation of node A due to part of the charge in the channel formation region flowing into node A.

On the other hand, by making the channel width W of the charge injection transistor smaller than the channel width W of the leakage current evaluation transistor, the leakage current of the charge injection transistor can be relatively reduced. In addition, the influence of voltage fluctuation at the node A due to a part of the charge in the channel formation region flowing into the node A during charge injection is small.

Next, a method for measuring leakage current of the characteristic evaluation circuit illustrated in FIG. 8A will be described with reference to FIG. FIG. 8B is a timing chart for explaining a leakage current measurement method using the characteristic evaluation circuit shown in FIG.

The leakage current measurement method using the characteristic evaluation circuit illustrated in FIG. 8A is divided into a writing period and a holding period. The operation in each period will be described below.

In the writing period, a voltage VL (−3 V) that turns off the transistor 812 is input as the voltage Vext_b. In addition, after the write voltage Vw is input as the voltage V1, a voltage VH (5 V) that turns on the transistor 811 for a certain period is input as the voltage Vext_a. As a result, charges are accumulated in the node A, and the voltage of the node A becomes equal to the write voltage Vw. After that, a voltage VL that turns off the transistor 811 is input as the voltage Vext_a. Thereafter, the voltage VSS (0 V) is input as the voltage V1.

In the holding period, the amount of change in the voltage of the node A caused by the change in the amount of charge held by the node A is measured. From the amount of change in voltage, the value of the current flowing between the source electrode and the drain electrode of the transistor 812 can be calculated. As described above, charge accumulation at the node A and measurement of the amount of change in the voltage at the node A can be performed.

At this time, accumulation of charge at the node A and measurement of the amount of change in the voltage at the node A (also referred to as accumulation and measurement operation) are repeatedly performed. First, the first accumulation and measurement operation is repeated 15 times. In the first accumulation and measurement operation, a voltage of 5 V is input as the writing voltage Vw during the writing period, and holding for one hour is performed during the holding period. Next, the second accumulation and measurement operation is repeated twice. In the second accumulation and measurement operation, a voltage of 3.5 V is input as the writing voltage Vw in the writing period, and holding for 50 hours is performed in the holding period. Next, the third accumulation and measurement operation is performed once. In the third accumulation and measurement operation, a voltage of 4.5 V is input as the writing voltage Vw in the writing period, and holding is performed for 10 hours in the holding period. By repeatedly accumulating and measuring, it is possible to confirm that the measured current value is a value in a steady state. In other words, among the current I _A flowing through the node A, it is possible to remove the transient current (current component decreases with the passage after the measurement start time). As a result, the leak current can be measured with higher accuracy.

In general, the voltage V _A at the node A is expressed as the equation (1) as a function of the output voltage Vout.

In addition, the charge Q _A of the node A is expressed as in Expression (2) using the voltage V _{A of} the node A, the capacitance C _A connected to the node A, and a constant (const). Here, the capacitance C _A connected to the node A, is the sum of the capacity component other than capacitance and the capacitor 813 of the capacitor 813.

Current I _A of the node A, since the time derivative of charge flowing to the node A (or node A charge flowing from), the current I _A of the node A is expressed by the equation (3).

Here, as an example, Δt is about 54000 sec. Thus, the capacitor C _A connected to the node A, the output voltage Vout, it is possible to obtain a current I _A of the node A is leakage current, it is possible to determine the leakage current of the circuit for evaluating characteristics.

Next, the measurement result of the output voltage by the measurement method using the characteristic evaluation circuit and the value of the leakage current of the characteristic evaluation circuit calculated from the measurement result will be described with reference to FIG.

FIG. 9A shows, as an example, the relationship between the elapsed time Time related to the above measurement (first accumulation and measurement operation) of the transistors in SMP4, SMP5, and SMP6 and the output voltage Vout. ) are shown and elapsed time time in the measurement, the relationship between the current I _a calculated by the measurement. It can be seen that the output voltage Vout has fluctuated since the start of measurement, and it takes 10 hours or more to reach a steady state.

FIG. 10 shows the relationship between the voltage of the node A and the leakage current in SMP1 to SMP6 estimated from the values obtained by the above measurement. In FIG. 10, for example, in SMP4, when the voltage at the node A is 3.0 V, the leakage current is 28 yA / μm. Since the leakage current includes the off-state current of the transistor 812, the off-state current of the transistor 812 can also be regarded as 28 yA / μm or less.

11, FIG. 12, and FIG. 13 show the relationship between the voltage of the node A and the leakage current in SMP1 to SMP6 estimated by the above measurement at 85 ° C., 125 ° C., and 150 ° C. As shown in FIGS. 11 to 13, it can be seen that even at 150 ° C., the leakage current is 100 zA / μm or less.

As described above, in a circuit for evaluating characteristics using a transistor that functions as a channel formation layer and includes a highly purified oxide semiconductor layer, the leakage current is sufficiently low; It turns out that it is small enough. It can also be seen that the off-state current of the transistor is sufficiently low even when the temperature rises.

(Embodiment 7)
In this embodiment, a structural example of the input / output device in the above embodiment will be described.

The input / output device in this embodiment is provided between a first substrate (an active matrix substrate) provided with a semiconductor element such as a transistor, a second substrate, and the first substrate and the second substrate. A liquid crystal layer.

First, structural examples of the active matrix substrate in this embodiment will be described with reference to FIGS. 14 and 15 are diagrams illustrating a structure example of an active matrix substrate in the input / output device of this embodiment, FIG. 14A is a schematic plan view, and FIG. 14B is a diagram of FIG. 15A is a schematic cross-sectional view taken along line AB in FIG. 15A, FIG. 15A is a schematic plan view, and FIG. 15B is a schematic cross-sectional view taken along line CD in FIG. FIG. Note that FIG. 15 illustrates the case where the photodetector circuit having the structure illustrated in FIG. 3A is used as an example of the photodetector circuit. 14 and 15 illustrate the case where the transistor having the structure described with reference to FIG. 6A is used as an example of the transistor.

14 and 15 includes a substrate 500, conductive layers 501a to 501h, an insulating layer 502, semiconductor layers 503a to 503d, conductive layers 504a to 504k, and an insulating layer. 505, a semiconductor layer 506, a semiconductor layer 507, a semiconductor layer 508, an insulating layer 509, and conductive layers 510a to 510c.

Each of the conductive layers 501 a to 501 h is provided on one plane of the substrate 500.

The conductive layer 501a functions as a gate of a display selection transistor in the display circuit.

The conductive layer 501b functions as a first capacitor electrode of a storage capacitor in the display circuit. Note that a layer functioning as a first capacitor electrode of a capacitor (retention capacitor) is also referred to as a first capacitor electrode.

The conductive layer 501c functions as a wiring through which the voltage Vb is input. Note that a layer having a function as a wiring is also referred to as a wiring.

The conductive layer 501d functions as the gate of the light detection control transistor in the light detection circuit.

The conductive layer 501e functions as a signal line through which a light detection control signal is input. Note that a layer having a function as a signal line is also referred to as a signal line.

The conductive layer 501f functions as the gate of the output selection transistor in the photodetector circuit.

The conductive layer 501g functions as the gate of the amplification transistor in the light detection circuit.

The insulating layer 502 is provided over one surface of the substrate 500 with the conductive layers 501a to 501h interposed therebetween.

The insulating layer 502 includes a gate insulating layer of a display selection transistor in the display circuit, a dielectric layer of a storage capacitor in the display circuit, a gate insulating layer of a light detection control transistor in the light detection circuit, a gate insulating layer of an amplification transistor in the light detection circuit, And functions as a gate insulating layer of the output selection transistor in the photodetector circuit.

The semiconductor layer 503a overlaps with the conductive layer 501a with the insulating layer 502 interposed therebetween. The semiconductor layer 503a functions as a channel formation layer of the display selection transistor in the display circuit.

The semiconductor layer 503b overlaps with the conductive layer 501d with the insulating layer 502 interposed therebetween. The semiconductor layer 503b functions as a channel formation layer of the light detection control transistor in the light detection circuit.

The semiconductor layer 503c overlaps with the conductive layer 501f with the insulating layer 502 interposed therebetween. The semiconductor layer 503c functions as a channel formation layer of the output selection transistor in the photodetector circuit.

The semiconductor layer 503d overlaps with the conductive layer 501g with the insulating layer 502 interposed therebetween. The semiconductor layer 503d functions as a channel formation layer of the amplification transistor in the photodetector circuit.

The conductive layer 504a is electrically connected to the semiconductor layer 503a. The conductive layer 504a functions as one of a source and a drain of the display selection transistor in the display circuit.

The conductive layer 504b is electrically connected to the conductive layer 501b and the semiconductor layer 503a. The conductive layer 504b functions as the other of the source and the drain of the display selection transistor in the display circuit.

The conductive layer 504c overlaps with the conductive layer 501b with the insulating layer 502 interposed therebetween. The conductive layer 504c functions as a second capacitor electrode of a storage capacitor in the display circuit.

The conductive layer 504d is electrically connected to the conductive layer 501c through an opening that penetrates the insulating layer 502. The conductive layer 504d functions as one of a first current terminal and a second current terminal of the photoelectric conversion element in the photodetector circuit.

The conductive layer 504e is electrically connected to the semiconductor layer 503b. The conductive layer 504e functions as one of a source and a drain of the light detection control transistor in the light detection circuit.

The conductive layer 504f is electrically connected to the semiconductor layer 503b and electrically connected to the conductive layer 501g in an opening that penetrates the insulating layer 502. The conductive layer 504f functions as the other of the source and the drain of the light detection control transistor in the light detection circuit.

The conductive layer 504g is electrically connected to the conductive layer 501d and the conductive layer 501e in an opening that penetrates the insulating layer 502. The conductive layer 504g functions as a signal line through which a light detection control signal is input.

The conductive layer 504h is electrically connected to the semiconductor layer 503c. The conductive layer 504h functions as one of a source and a drain of the output selection transistor in the photodetector circuit.

The conductive layer 504i is electrically connected to the semiconductor layer 503c and the semiconductor layer 503d. The conductive layer 504 i functions as the other of the source and the drain of the output selection transistor in the photodetector circuit and the one of the source and the drain of the amplification transistor in the photodetector circuit.

The conductive layer 504j is electrically connected to the semiconductor layer 503d, and is electrically connected to the conductive layer 501h in an opening that penetrates the insulating layer 502. The conductive layer 504j functions as the other of the source and the drain of the amplification transistor in the photodetector circuit.

The conductive layer 504k is electrically connected to the conductive layer 501h in an opening that penetrates the insulating layer 502. The conductive layer 504k functions as a wiring through which the voltage Va or the voltage Vb is input.

The insulating layer 505 is in contact with the semiconductor layers 503a to 503d through the conductive layers 504a to 504k.

The semiconductor layer 506 is electrically connected to the conductive layer 504d through an opening provided through the insulating layer 505.

The semiconductor layer 507 is in contact with the semiconductor layer 506.

The semiconductor layer 508 is in contact with the semiconductor layer 507.

The insulating layer 509 overlaps with the insulating layer 505, the semiconductor layer 506, the semiconductor layer 507, and the semiconductor layer 508. The insulating layer 509 functions as a planarization insulating layer in the display circuit and the photodetector circuit. Note that the insulating layer 509 is not necessarily provided.

The conductive layer 510a is electrically connected to the conductive layer 504b through an opening that penetrates the insulating layer 505 and the insulating layer 509. The conductive layer 510a functions as a pixel electrode of a display element in the display circuit. Note that a layer having a function as a pixel electrode is also referred to as a pixel electrode.

The conductive layer 510b is electrically connected to the conductive layer 504c through an opening that penetrates the insulating layer 505 and the insulating layer 509. The conductive layer 510b functions as a wiring through which the voltage Vc is input.

The conductive layer 510 c is electrically connected to the conductive layer 504 e through an opening that penetrates the insulating layers 505 and 509, and is electrically connected to the semiconductor layer 508 through an opening that penetrates the insulating layers 505 and 509. The

Further, an example of the structure of the input / output device in this embodiment is described with reference to FIGS. FIG. 16 is a cross-sectional schematic diagram illustrating a structural example of the input / output device in this embodiment, FIG. 16A is a schematic cross-sectional view of a display circuit, and FIG. It is a cross-sectional schematic diagram. As an example, the display element is a liquid crystal element.

The input / output device illustrated in FIG. 16 includes a substrate 512, a conductive layer 513, and a liquid crystal layer 514 in addition to the active matrix substrate illustrated in FIGS.

The conductive layer 513 is provided on one plane of the substrate 512. The conductive layer 513 functions as a common electrode in the display circuit. Note that the conductive layer 513 is not necessarily provided in the light detection circuit.

The liquid crystal layer 514 is provided between the conductive layer 510 a and the conductive layer 513 and overlaps with the semiconductor layer 508 with the insulating layer 509 interposed therebetween.

Note that the conductive layer 510a, the liquid crystal layer 514, and the conductive layer 513 function as display elements in the display circuit.

Further, each component of the input / output device shown in FIG. 16 will be described.

As the substrate 500 and the substrate 512, a substrate applicable to the substrate 400a in FIG. 6A can be used.

As the conductive layers 501a to 501h, a layer of a material that can be used for the conductive layer 401a in FIG. 6A can be used. Alternatively, the conductive layers 501a to 501h may be formed by stacking layers of materials that can be used for the conductive layer 401a.

As the insulating layer 502, a layer of a material that can be used for the insulating layer 402a in FIG. 6A can be used. Alternatively, the insulating layer 502 may be formed by stacking layers of materials that can be used for the insulating layer 402a.

As the semiconductor layers 503a to 503d, a layer of a material that can be used for the oxide semiconductor layer 403a illustrated in FIG. 6A can be used. Note that as the semiconductor layers 503a to 503d, semiconductor layers using a Group 14 semiconductor (such as silicon) in the periodic table may be used.

As the conductive layers 504a to 504k, a layer formed using a material that can be used for the conductive layer 405a or the conductive layer 406a in FIG. 6A can be used. Alternatively, the conductive layers 504a to 504k may be formed by stacking layers of materials applicable to the conductive layer 405a or the conductive layer 406a.

As the insulating layer 505, a layer of a material that can be used for the oxide insulating layer 407a in FIG. 6A can be used. Alternatively, the insulating layer 505 may be formed by stacking layers applicable to the oxide insulating layer 407a.

The semiconductor layer 506 is a semiconductor layer of one conductivity type (one of P-type and N-type). As the semiconductor layer 506, for example, a semiconductor layer containing silicon can be used.

The semiconductor layer 507 is a semiconductor layer having higher resistance than the semiconductor layer 506. As the semiconductor layer 507, for example, a semiconductor layer containing silicon can be used.

The semiconductor layer 508 is a semiconductor layer having a different conductivity type from the semiconductor layer 506 (the other of P-type and N-type). As the semiconductor layer 508, for example, a semiconductor layer containing silicon can be used.

As the insulating layer 509, a layer of an organic material such as polyimide, acrylic, or benzocyclobutene can be used, for example. As the insulating layer 509, a layer of a low dielectric constant material (also referred to as a low-k material) can be used.

As the conductive layers 510a to 510c and the conductive layer 513, for example, a light-transmitting conductive material layer can be used. As the light-transmitting conductive material, for example, indium tin oxide or indium oxide is oxidized. Metal oxide mixed with zinc (also called IZO: indium zinc oxide), conductive material mixed with indium oxide and silicon oxide (SiO ₂ ), organic indium, organic tin, indium oxide containing tungsten oxide, tungsten oxide included Indium zinc oxide, indium oxide containing titanium oxide, indium tin oxide containing titanium oxide, or the like can be used.

The conductive layers 510a to 510c and the conductive layer 513 can also be formed using a conductive composition including a conductive high molecule (also referred to as a conductive polymer). The conductive layer formed using the conductive composition preferably has a sheet resistance of 10,000 Ω / □ or less and a light transmittance of 70% or more at a wavelength of 550 nm. Moreover, it is preferable that the resistivity of the conductive polymer contained in the conductive composition is 0.1 Ω · cm or less.

As the conductive polymer, a so-called π-electron conjugated conductive polymer can be used. Examples of the π-electron conjugated conductive polymer include polyaniline or a derivative thereof, polypyrrole or a derivative thereof, polythiophene or a derivative thereof, or a copolymer of two or more of aniline, pyrrole, and thiophene or a derivative thereof.

As the liquid crystal layer 514, for example, a layer containing TN liquid crystal, OCB liquid crystal, STN liquid crystal, VA liquid crystal, ECB liquid crystal, GH liquid crystal, polymer dispersed liquid crystal, discotic liquid crystal, or the like can be used. Note that as the liquid crystal layer 514, a liquid crystal that transmits light when voltage applied to the conductive layers 510 c and 513 is 0 V is preferably used.

As described with reference to FIGS. 14 to 16, the structure example of the input / output device in this embodiment includes an active matrix substrate including a transistor, a pixel electrode, and a photoelectric conversion element, a counter substrate, an active matrix substrate, And a liquid crystal layer having liquid crystal between opposing substrates. With the above structure, a display circuit and a photodetector circuit can be manufactured over the same substrate in the same process, so that manufacturing costs can be reduced.

(Embodiment 8)
In this embodiment, an electronic device including the input / output device in the above embodiment is described.

An example of a structure of the electronic device in this embodiment will be described with reference to FIGS. 17A to 17F are diagrams each illustrating an example of a structure of the electronic device in this embodiment.

An electronic device illustrated in FIG. 17A is a portable information communication terminal. A portable information communication terminal illustrated in FIG. 17A includes at least an input / output unit 1001. In the portable information communication terminal illustrated in FIG. 17A, for example, the operation unit 1002 can be provided in the input / output unit 1001. For example, by using the input / output device of the above embodiment for the input / output unit 1001, the portable information communication terminal can be operated or information can be input to the portable information communication terminal, for example, with a finger or a pen.

The electronic device illustrated in FIG. 17B is an information guidance terminal including car navigation, for example. An information guidance terminal illustrated in FIG. 17B includes an input / output unit 1101, operation buttons 1102, and an external input terminal 1103. For example, by using the input / output device of the above embodiment for the input / output unit 1101, the information guide terminal can be operated or information can be input to the information guide terminal with a finger or a pen, for example.

An electronic device illustrated in FIG. 17C is a laptop personal computer. A notebook personal computer illustrated in FIG. 17C includes a housing 1201, an input / output portion 1202, a speaker 1203, an LED lamp 1204, a pointing device 1205, a connection terminal 1206, and a keyboard 1207. . For example, by using the input / output device of the above embodiment for the input / output unit 1202, it is possible to operate a notebook personal computer or input information to the notebook personal computer, for example, with a finger or a pen. Further, the input / output device of the above embodiment may be used for the pointing device 1205.

An electronic device illustrated in FIG. 17D is a portable game machine. A portable game machine shown in FIG. 17D includes an input / output unit 1301, an input / output unit 1302, a speaker 1303, a connection terminal 1304, an LED lamp 1305, a microphone 1306, a recording medium reading unit 1307, An operation button 1308 and a sensor 1309 are provided. For example, by using the input / output device of the above embodiment for the input / output unit 1301 and the input / output unit 1302, or the input / output unit 1301 or the input / output unit 1302, the portable game machine can be operated or carried with a finger or a pen, for example. It is possible to input information to the type gaming machine.

The electronic device illustrated in FIG. 17E is an electronic book. An electronic book illustrated in FIG. 17E includes at least a housing 1401, a housing 1403, an input / output portion 1405, an input / output portion 1407, and a shaft portion 1411.

The housing 1401 and the housing 1403 are connected to each other with a shaft portion 1411, and the electronic book illustrated in FIG. 17E can open and close with the shaft portion 1411 as an axis. With such a configuration, an operation like a paper book can be performed. The input / output unit 1405 is incorporated in the housing 1401 and the input / output unit 1407 is incorporated in the housing 1403. Further, the configurations of the input / output unit 1405 and the input / output unit 1407 may be configured to display different images, for example, a configuration in which a series of images are displayed on both the input / output units. By configuring the input / output unit 1405 and the input / output unit 1407 to display different images, for example, a sentence image is displayed on the right input / output unit (the input / output unit 1405 in FIG. 17E), and the left input / output unit is displayed. An image can be displayed on the unit (input / output unit 1407 in FIG. 17E).

In the electronic book illustrated in FIG. 17E, the housing 1401 or the housing 1403 may include an operation portion and the like. For example, the structure of the electronic book illustrated in FIG. 17E can be a structure including a power button 1421, operation keys 1423, and a speaker 1425. The electronic book illustrated in FIG. 17E can send a page of an image having a plurality of pages by using the operation keys 1423. Alternatively, a keyboard, a pointing device, or the like may be provided in the input / output unit 1405 and the input / output unit 1407 or the input / output unit 1405 or the input / output unit 1407 of the electronic book illustrated in FIG. 17E can be connected to an external connection terminal (an earphone terminal, a USB terminal, or various cables such as an AC adapter or a USB cable) on the back surface or the side surface of the housing 1401 and the housing 1403 of the e-book reader. A terminal or the like), a recording medium insertion portion, or the like may be provided. Further, the electronic book illustrated in FIG. 17E may have a function as an electronic dictionary.

For example, by using the input / output device of the above embodiment for the input / output unit 1405 and the input / output unit 1407, or the input / output unit 1405 or the input / output unit 1407, for example, an electronic book can be operated with a finger or a pen Information can be entered.

The electronic device illustrated in FIG. 17F is a display. A display illustrated in FIG. 17F includes a housing 1501, an input / output portion 1502, a speaker 1503, an LED lamp 1504, an operation button 1505, a connection terminal 1506, a sensor 1507, a microphone 1508, and a support base. 1509. For example, by using the input / output device of the above embodiment for the input / output unit 1502, the display can be operated or information can be input to the display with a finger or a pen, for example.

As described with reference to FIGS. 17A and 17B, the electronic device in this embodiment includes an input / output portion using the input / output device of the above embodiment. With the above structure, the influence of light in an environment where the electronic device is placed can be suppressed, and the light detection accuracy of the input / output unit can be improved.

101 Display Selection Signal Output Circuit 102 Display Data Signal Output Circuit 103a Photodetection Reset Signal Output Circuit 103b Photodetection Control Signal Output Circuit 103c Output Selection Signal Output Circuit 104a Light Unit 104b Light Unit 105 Pixel Unit 105d Display Circuit 105p Photodetection Circuit 106 Read Circuit 107 data processing circuit 131a photoelectric conversion element 131b photoelectric conversion element 132a transistor 132b transistor 133a transistor 133b transistor 134a transistor 134b transistor 135 transistor 151a transistor 151b transistor 152a liquid crystal element 152b liquid crystal element 153a capacitor element 153b capacitor element 154 capacitor element 155 transistor 156 transistor 201 light source 202 light guide plate 203 fixing material 20 Finger 205 Pixel 400a substrate 400b substrate 400c substrate 400d substrate 401a conductive layer 401b conductive layer 401c conductive layer 401d conductive layer 402a insulating layer 402b insulating layer 402c insulating layer 402d insulating layer 403a oxide semiconductor layer 403b oxide semiconductor layer 403c oxide semiconductor Layer 403d oxide semiconductor layer 405a conductive layer 405b conductive layer 405c conductive layer 405d conductive layer 406a conductive layer 406b conductive layer 406c conductive layer 406d conductive layer 407a oxide insulating layer 407b oxide insulating layer 407c oxide insulating layer 447 insulating layer 500 substrate 501a Conductive layer 501b Conductive layer 501c Conductive layer 501d Conductive layer 501e Conductive layer 501f Conductive layer 501g Conductive layer 501h Conductive layer 502 Insulating layer 503a Semiconductor layer 503b Semiconductor layer 503c Semiconductor layer 503d Semiconductor layer 504a Conductive layer 504b Conductive layer 504c Conductive layer 504d Conductive layer 504e Conductive layer 504f Conductive layer 504g Conductive layer 504h Conductive layer 504i Conductive layer 504j Conductive layer 504k Conductive layer 505 Insulating layer 506 Semiconductor layer 507 Semiconductor layer 508 Insulating layer 509 510a Conductive layer 510b Conductive layer 510c Conductive layer 512 Substrate 513 Conductive layer 514 Liquid crystal layer 801 Measurement system 811 Transistor 812 Transistor 813 Capacitance element 814 Transistor 815 Transistor 1001 Input / output unit 1002 Operation unit 1101 Input / output unit 1102 Operation button 1103 External input terminal 1201 Case 1202 Input / output unit 1203 Speaker 1204 LED lamp 1205 Pointing device 1206 Connection terminal 1207 Keyboard 1301 Input / output unit 1302 Output unit 1303 Speaker 1304 Connection terminal 1305 LED lamp 1306 Microphone 1307 Recording medium reading unit 1308 Operation button 1309 Sensor 1401 Case 1403 Case 1405 Input / output unit 1407 Input / output unit 1411 Shaft portion 1421 Power button 1423 Operation key 1425 Speaker 1501 Case 1502 Input / output unit 1503 Speaker 1504 LED lamp 1505 Operation button 1506 Connection terminal 1507 Sensor 1508 Microphone 1509 Support stand

Claims (2)

A first light unit having light emitting diodes emitting red, blue and green;
A second light unit having a light emitting diode emitting white light;
A display circuit;
An input / output device having a photodetection circuit,
The display circuit and the light detection circuit are sandwiched between the first light unit and the second light unit,
The input / output device is driven in a field sequential manner using light from the first light unit,
During the period when the first light unit is turned off, the second light unit is turned on,
The input / output device, wherein the light detection circuit generates data corresponding to an illuminance of light from the second light unit. A first light unit having light emitting diodes emitting red, blue and green;
A second light unit having a light emitting diode emitting white light;
A display circuit;
An input / output device having a photodetection circuit,
The display circuit and the light detection circuit are sandwiched between the first light unit and the second light unit,
The input / output device is driven in a field sequential manner using light from the first light unit,
During the period when the first light unit is turned off, the second light unit is turned on,
The light detection circuit generates data corresponding to the illuminance of light from the second light unit,
The first data generated by the light detection circuit during the period when the second light unit is turned on, and the light detection circuit is generated during the period when the first light unit and the second light unit are turned off. An input / output device that compares the second data to generate third data that is difference data between the first data and the second data.